Most of electronic devices generate heat while they are used, so that the removal of the generated heat therefrom is necessary for their normal operation. For the reduction of the heat from electronic devices, it has been expected to make good use of aluminum nitride having high thermal conductivity and excellent electric insulating properties. In applying it to electronic devices, the aluminum nitride can be used in various forms, including moldings and fillers for grease and synthetic rubber.
However, aluminum nitride is inferior in water resistance, particularly in a pulverized state. More specifically, the aluminum nitride in pulverized state is gradually decomposed while it is allowed to stand in the air, thereby evolving ammonia to be converted into aluminum hydroxide. Therefore, the problem confronting the use of an aluminum nitride powder, e.g., as a filler for heat reduction of resins is poor water resistance of the powder.
For improving the water resistance of an aluminum nitride powder, some attempts have been made. For instance, the improvement of water resistance has been attempted by coating the surface of an aluminum nitride powder with an organic high molecular compound, or by oxidizing the aluminum nitride powder surface to form a protective film of aluminum oxide. Further, Japanese Tokkai Hei 4-321506 (the term "Tokkai" as used herein means an "unexamined published patent application") proposes the art of forming a coating on the aluminum nitride powder surface through the reaction between an organosilane oligomer and an silanol group-containing polyorganosiloxane in the presence of a catalyst.
However, none of those methods are successful in conferring sufficient water resistance upon aluminum nitride. Thus, the application of such aluminum nitride powders to a silicone grease composition for heat reduction use has a defect that the resulting composition suffers gradual deterioration in heat reduction characteristics.